The prior art describes a variety of methods for the construction of circular metal tanks used in storage of solids or liquids. For instance, U.S. Pat. No. 2,751,672, issued to Reed, describes the fabrication of circular tanks from a series of metal sheets which are bolted together. This method of assembly requires a large amount of manual labour, a complicated tank support structure, and is unsuitable for producing tanks for storage of liquids due to the massive number of bolt holes requiring hydraulic seals to prevent the leakage of any stored liquid.
U.S. Pat. No. 4,121,747, issued to McFatter, describes the construction of circular storage tanks from strip metal wound in a helical path in which the tank is built upwardly. The metal strip is fed to a support assembly arranged circularly on a base, and the upper edge of the strip that is fed to the support assembly is aligned with the lower edge of the helical turn immediately thereabove so that the edges are spaced apart in a vertical plane from each other and then “butt” welded together. This invention teaches away from the bending of metal strip edges and sees no potential advantage in doing so. This technique for tank fabrication suffers from the following disadvantages:                a) satisfactory alignment of metal strips ahead of a butt welder is difficult;        b) slight misalignment of the metal strips, especially for thinner metal thicknesses, can cause weak welds and/or leaks due to insufficient metal-to-metal contact; and        c) there is no provision for reinforcement of metal strips to prevent their deformation (e.g. bulging due to pressure on lower metal strips in a tall liquid storage tank.        
U.S. Pat. No. 3,863,479 to Lipp describes the fabrication of metal tubes and tanks from helical metal coils using severe folded bends from adjacent coils. Lipp suffers from the following disadvantages:                a) the tanks are unsuitable for storage of liquids since perfect hydraulic seals at the mechanical bends cannot be guaranteed;        b) the method is unsuitable for hard-to-bend metals, especially for higher carbon steels, due to the severity of the bends and lack of stress relief (e.g. annealing) after bending resulting in potential metal cracking and subsequent loss of strength and hydraulic seals;        c) the thickness of usable metal is limited due to the severity of the bends, which may result in cracking and subsequent loss of strength and hydraulic seals; and        d) there are no reinforcing corrugations in the coils to prevent bulging, which is especially problematic since the thickness of the metal that may be used is limited, as discussed in point (c) above.        